Cardiac rhythm management system and method

ABSTRACT

A system and method for cardiac rhythm management, which includes an electrode system having at least one electrode and control circuitry coupled to the electrode system from which a first cardiac signal is sensed. The control circuitry includes a pulse circuit to produce electrical pulses at a first value to be delivered to the electrode system in a first cardiac region. At least one cardiac signal is sensed from a second cardiac region, where the cardiac signal includes indications of cardiac depolarizations from the second cardiac region which occurs in direct reaction to the electrical pulses delivered to the first cardiac region. The first value of the electrical pulses are then modified by a pulse adjustment circuit when a cardiac depolarization which occurs in direct reaction to the electrical pulse delivered to the first cardiac region is detected from the second cardiac region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 10/858,580, filed on Jun. 2, 2004, which is a continuation ofU.S. patent application Ser. No. 10/059,771, filed on Jan. 28, 2002, nowissued as U.S. Pat. No. 6,928,325, which is a continuation of U.S.patent application Ser. No. 09/571,786, filed on May 16, 2000, nowissued as U.S. Pat. No. 6,363,281, the specifications of which areincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

This invention relates generally to the field of medical devices, andmore particularly to an implantable cardiac rhythm management devicewhich generates electrical pulses.

BACKGROUND

The heart is generally divided into four chambers, two atrial chambersand the two ventricular chambers. As the heart beats, the atrialchambers and the ventricular chambers of the heart go through a cardiaccycle. The cardiac cycle consists of one complete sequence ofcontraction and relaxation of the chambers of the heart.

The terms systole and diastole are used to describe the contraction andrelaxation phases the chambers of the heart experience during a cardiaccycle. In systole, the ventricular muscle cells are contracting to pumpblood through the circulatory system. During diastole, the ventricularmuscle cells relax, causing blood from the atrial chambers to fill theventricular chambers. After the period of diastolic filling, thesystolic phase of a new cardiac cycle is initiated. Control over thetiming and order of the atrial and ventricular contractions during thecardiac cycle is critical for the heart to pump blood efficiently.Efficient pumping action of the heart requires precise coordination ofthe contraction of individual cardiac muscle cells.

Implantable cardiac pacemakers have been successfully used to maintaincontrol over the timing and order of the cardiac cycle. In its simplestform, the cardiac pacemaker is an electrical circuit in which a batteryprovides electricity that travels through a cardiac lead to a cardiacelectrode and into the heart causing a contraction, and back to thebattery to complete the circuit. Cardiac electrodes are typicallyimplanted within or adjacent one cardiac chamber. This allows forcardiac signals to be sensed predominately from that chamber and forelectrical energy pulses to be delivered to that chamber. For example,tip electrodes on transvenous leads are typically implanted in the apexof the right ventricular chamber or at or near the atrial appendage ofthe right atrium. Because the tip electrode is implanted completelywithin one cardiac chamber, electrical pulses provided through the tipelectrode stimulate the chamber in which the electrode is implanted. So,for example, a pacing pulse delivered to an atrial electrode implantedin the atrial appendage stimulates the atria to contract. Likewise, apacing pulse delivered to a ventricular electrode implanted in the rightventricle apex stimulates the ventricles to contract.

A current trend in cardiac rhythm management devices, also referred toas implantable pulse generator systems, is to implant cardiac electrodesin and/or through the coronary sinus vein. The coronary sinus veindrains venous blood from the coronary arteries into the right atrium.The coronary sinus vein also allows access to cardiac locations that areadjacent to either the left atrium and/or the left ventricle, whereaccess to the left ventricle is typically gained through the greatcardiac vein which is coupled to the coronary sinus vein. As such, thecoronary sinus vein is an avenue for accessing, sensing and providingstimulation to different sites of the heart.

One difficulty encountered when using transvenous electrodes implantedwithin the coronary sinus is that electrical pulses delivered to capturethe atrium can also capture the ventricles, or visa versa. Thissituation is referred to as “cross capture.” Cross capture arises fromthe fact that the coronary sinus is generally located between the atrialchambers and the ventricular chambers along the anterior groove. Whentransvenous electrodes are positioned in this region of the heart it ispossible for electrical pulses intended to stimulate the atrial chamberto instead, or in addition to, stimulate the ventricular chamber. Thissituation is undesirable, as hemodynamic efficiency is adverselyeffected when the ventricles contract too soon with respect to theatrial chambers. Thus, a need exists for a reliable way of preventingunintentional cross capture pacing.

SUMMARY OF THE INVENTION

The present subject matter provides a system and method to address theaforementioned problems. In one embodiment, the present subject matterutilizes autocapture protocols to monitor the capture of both atrium andventricle chambers in response to electrical energy supplied to one ormore electrodes positioned in or around the coronary sinus vein.Depending upon which chambers of the heart are captured, the presentsubject matter uses the information to adjust the energy level of pulsessupplied to the one or more electrodes. Thus, the present subject mattercan be used to prevent unintentional cross capture pacing (i.e., toprevent pulses intended to capture the atria from instead capturing theventricles, and visa versa).

The present system provides for electrical pulses having a first valueto be delivered to a first cardiac region. The system also senses atleast one cardiac signal, where the cardiac signal includes indicationsof cardiac depolarizations resulting from the electrical pulses. In oneembodiment, the system detects in the first cardiac signal cardiacdepolarizations from a second cardiac region which occurs in directreaction to an electrical pulse delivered to the first cardiac region.When one or more cardiac depolarizations occurring in direct reaction toelectrical pulses delivered to the first cardiac region are detected inthe second cardiac region the first value of the electrical pulses aremodified so as to eliminate the depolarizations in the second cardiacregion caused as a direct reaction to the electrical pulses.

In one embodiment, the first cardiac region is a supraventricularlocation and the second cardiac region is a ventricular cardiac region,so that the system delivers the electrical pulses to thesupraventricular location and detects the cardiac signal from theventricular cardiac region. Alternatively, the first cardiac region isthe ventricular location and the second cardiac region is thesupraventricular cardiac region, so that the system delivers theelectrical pulses to the ventricular location and detects the cardiacsignal from the supraventricular cardiac region.

In one embodiment, threshold test is used to set the first value of theelectrical pulses. In one embodiment, test pacing pulses are deliveredfor the threshold test, where the values of the test pacing pulses aregreater than a first value range and include an initial high-test pacingpulse. The cardiac signal is analyzed for cardiac depolarizations fromthe first cardiac region and the second cardiac region which occur as aresult of the initial high-test pacing pulse. The values of the testpacing pulses are then reduced over the first value range until a secondcardiac region pacing threshold value is reached where the secondcardiac region is no longer depolarized and the first cardiac region isdepolarized by the test pacing pulses. The values of the test pacingpulses continue to be reduced over the first value range until a firstcardiac region pacing threshold value is reached where both the firstcardiac region and the second cardiac region are no longer depolarizedby the test pacing pulses. The first value of the pacing pulses is thenset based on the first cardiac region pacing threshold value and thesecond cardiac region pacing threshold value.

In an alternative embodiment, the threshold test includes deliveringtest pacing pulses, including an initial low-test pacing pulse, atvalues over a first value range to the first cardiac region. The cardiacsignal is then analyzed for cardiac depolarizations from the firstcardiac region and the second cardiac region which occur as a result ofthe initial low-test pacing pulse. The values of the test pacing pulsesare then increased over the first value range until a first cardiacregion pacing threshold value is reached where the first cardiac regionis depolarized and the second cardiac region is not depolarized by thetest pacing pulses. The values of the test pacing pulses are continuedto be increased over the first value range until a second cardiac regionpacing threshold value is reached where both the first cardiac regionand the second cardiac region are depolarized by the test pacing pulses.The first value is then set based on the first cardiac region pacingthreshold value and the second cardiac region pacing threshold value.

These and other features and advantages of the invention will becomeapparent from the following description of the preferred embodiments ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of pacing threshold values versus electrode positionsaccording to the present subject matter;

FIG. 2 is a flow chart illustrating one embodiment of the presentsubject matter;

FIG. 3 is a schematic diagram according to one embodiment of the presentsubject matter;

FIG. 4 is a flow chart illustrating one embodiment of the presentsubject matter;

FIG. 5 is a flow chart illustrating one embodiment of the presentsubject matter;

FIG. 6 is a flow chart illustrating one embodiment of the presentsubject matter;

FIG. 7 is a schematic view of one embodiment of an implantable medicaldevice according to one embodiment of the present subject matter; and

FIG. 8 is a block diagram of one embodiment of an implantable medicaldevice according to the present subject matter.

DETAILED DESCRIPTION

In the following detailed description, references are made to theaccompanying drawings that illustrate specific embodiments in which theinvention may be practiced. Electrical, mechanical, programmatic andstructural changes may be made to the embodiments without departing fromthe spirit and scope of the present invention. The following detaileddescription is, therefore, not to be taken in a limiting sense and thescope of the present invention is defined by the appended claims andtheir equivalents.

Typically, transvenous electrodes are implanted within one cardiacchamber. This allows for cardiac signals to be sensed predominately fromthat chamber and for electrical energy pulses to be delivered to thatchamber. For example, tip electrodes on transvenous leads are typicallyimplanted in the apex of the right ventricular chamber or at or near theatrial appendage of the right atrium. Because the tip electrode isimplanted completely within one cardiac chamber, electrical pulsesprovided through the tip electrode stimulate the chamber in which theelectrode is implanted. So, for example, a pacing pulse delivered to anatrial electrode implanted in the atrial appendage stimulates the atriato contract. Likewise, a pacing pulse delivered to a ventricularelectrode implanted in the right ventricle apex stimulates theventricles to contract.

A current trend in cardiac rhythm management devices, also referred toas implantable pulse generator systems, is to implant cardiac electrodesin and/or through the coronary sinus vein. The coronary sinus veindrains venous blood from the coronary arteries into the right atrium.The coronary sinus vein also allows access to cardiac locations that areadjacent to either the left atrium and/or the left ventricle, whereaccess to the left ventricle is typically gained through the greatcardiac vein which is coupled to the coronary sinus vein. As such, thecoronary sinus vein is an avenue for accessing, sensing and providingstimulation to different sites of the heart.

One difficulty encountered when using transvenous electrodes implantedwithin the coronary sinus is that electrical pulses delivered to capturethe atrium can also capture the ventricles. This difficulty arises fromthe fact that the coronary sinus is generally located between the atrialchambers and the ventricular chambers along the anterior groove. Whentransvenous electrodes are positioned in this region of the heart it ispossible for electrical pulses intended to stimulate the atrial chamberto instead, or in addition to, stimulate the ventricular chamber. Thissituation is undesirable, as hemodynamic efficiency is adverselyeffected when the ventricles contract too soon with respect to theatrial chambers.

The present subject matter provides a system and method to address theaforementioned problems. In one embodiment, the present subject matterutilizes autocapture protocols, described below, to monitor the captureof both atrium and ventricle chambers in response to electrical energysupplied to one or more electrodes positioned in or around the coronarysinus vein. Depending upon which chambers of the heart are captured, thepresent subject matter uses the information to adjust the energy levelof pulses supplied to the one or more electrodes. Thus, the presentsubject matter can be used to prevent unintentional cross capture pacing(i.e., to prevent pulses intended to capture the atria from insteadcapturing the ventricles, and visa versa).

Referring now to FIG. 1, there is shown a graph of atrial andventricular pacing thresholds as a function of electrode location withineither the coronary sinus or the great cardiac vein. Each pair of datapoints represent the atrial and ventricular pacing threshold fromproximal, middle and distal positions within the coronary sinus and thegreat coronary vein. In most locations, atrial capture threshold islower than the ventricular threshold, where the difference varies withlocation of the electrode location.

Research data, such as shown in FIG. 1, shows that stimulation pulsesfrom electrodes implanted in the coronary sinus vein or the greatcardiac vein are capable of capturing both the atrium and theventricles, depending upon the value of the pulses. For example, whenthe stimulation electrode was implanted in the proximal coronary sinus100, the difference in values of the stimulation pulses required tocapture the atrium and the ventricles was significantly smaller than thedifference in values of the stimulation pulses required to capture theatrium and the ventricles when the stimulation electrode was implantedin the distal portion of the coronary sinus 120. At 130, when theelectrode is implanted at a distal position in the great coronary vein,the data generally indicates that the atrial pacing threshold is greaterthan the ventricular pacing threshold.

These relative differences in pacing threshold of the atrium andventricles are important considerations in ensuring the intended chamberof the heart is paced from positions within the coronary sinus and thegreat cardiac vein. Leads may migrate within the coronary sinus or thegreat cardiac vein, changing the initial location of the electrode andthe threshold necessary to pace the intended chamber. In one embodiment,when the cardiac rhythm management device is programmed with a fixedpacing output for atrial pacing to one or more electrodes implanted inthe coronary sinus, migration of the electrodes within the coronarysinus or the great cardiac vein may cause either loss of capture of theatrium with the pacing pulses, capture of the ventricles or both.Changes in pacing threshold due to changes in location of the electrodeswithin the coronary sinus can also be exacerbated by changes inthreshold voltage that occur as the lead matures. Thus, over time thefixed pacing output for atrial pacing from the coronary sinus and/or thegreat cardiac vein can fail to be sufficient to capture the atria and/orbegin to capture the ventricles. The present subject matter addressesthese issues.

Referring now to FIG. 2, there is shown one embodiment of a method forthe present subject matter. At 200, electrical pulses having a firstvalue are delivered to a first cardiac region. In one embodiment, thefirst value of the electrical pulses is a voltage value which is usefulin capturing one or more cardiac chambers (e.g., atrial chambers orventricular chambers). Alternatively, the first value is a width of anelectrical pulse which is useful in capturing one or more cardiacchambers (e.g., atrial chambers or ventricular chambers). By way ofexample, and not by way of limitation, the electrical pulses used in thepresent subject matter are pacing level pulses. In one embodiment, thefirst value of the pacing level pulses are voltages in the range of 0.1to 10 volts. Alternatively, the first value for the pacing level pulsesare pacing pulses having a pulse width in the range of 0.1 to 20milliseconds.

In addition to delivering electrical pulses to the first cardiac region,at least one cardiac signal is also sensed at 210, where the cardiacsignal includes indications of cardiac depolarizations from the firstcardiac region and/or from a second cardiac region. In one embodiment,the cardiac signals are either unipolar signals sensed between anelectrode implanted in the heart and the housing of the cardiac rhythmmanagement device or an indifferent electrode mounted on or near thecardiac rhythm management device. Alternatively, the sensed signal is abipolar signal sensed between two electrodes implanted within the heart.

At 220, the cardiac signal containing indications of cardiacdepolarizations from the second cardiac region is analyzed to detect acardiac depolarization that occurs as a direct reaction to an electricalpulse delivered to the first cardiac region. In one embodiment, acardiac depolarization occurring in the second cardiac region as adirect reaction to a pulse delivered to the first cardiac region isidentified based on the short time duration between the delivery of thepulse and the occurrence of the depolarization in the second cardiacregion (e.g., a time duration shorter than AV-delay). Alternatively,autocapture systems and/or methods may be employed to identify cardiacdepolarizations occurring as a direct result of delivered pacing pulses.

Autocapture systems and/or methods have been suggested as a way ofidentifying evoked responses from sensed cardiac signals. One problemfaced by such systems is dealing with “afterpotential”, or polarizationvoltage. Typically, an “afterpotential”, or polarization voltage,develops in the cardiac tissue surrounding a pacing/sensing electrodeafter the electrode is used to deliver a pacing pulse. Theafterpotential typically has a voltage and a duration that is so largethat any response of the cardiac tissue evoked by the pacing pulse ismasked or buried within the afterpotential. This is an undesirableresult as verification of capture by an implantable pulse generator ishampered.

One example of an autocapture system and method for identifying evokeddepolarizations is where an “afterpotential”, or polarization voltage,resulting from a pacing pulse is attenuated to allow for the evokedresponse to be readily identified. In one embodiment, attenuation of theafterpotential is accomplished with an improved pacing output circuitwhich is the subject matter of a co-pending U.S. patent applicationentitled “Improved Pacing Output Coupling Capacitor for AutomaticCapture Threshold Detection In Cardiac Pacing Systems”, where theco-pending application is a Continuation-in-part application ofapplication Ser. No. 08/977,272, filed Nov. 24, 1997, entitled “PacingOutput Circuitry For Automatic Capture Threshold Detection In CardiacPacing Systems”, where all of the co-pending applications are herebyincorporated by reference in their entirety.

Referring now to FIG. 3, there is shown one embodiment of the pacingoutput circuit 300. The pacing output circuit 300 is shown havingswitches 302, 304, 306, 308, a pacing charge capacitor 310, a firstcoupling capacitor 312, and a second coupling capacitor 314, where thecircuit 300 is coupled to a power supply 316 and to sensing and pacingelectrodes 320 and 322. In one embodiment, sensing and pacing electrodes320 and 322 can have any number of configurations, including but notlimited to ring and/or tip electrodes. Additionally, the pacing chargecapacitor 310 can have a capacitance suitable for use in a pulsegenerator, where a capacitance of greater than 10 microfarads ispossible. The circuit 300 can be integrated into a cardiac rhythmmanagement system, including, but not limited to, pacemakers andimplantable cardioverter/defibrillators.

In the pacing output circuit 300, one function of the second couplingcapacitor 314 is to block DC signals from reaching a heart duringpacing. Additionally, the second coupling capacitor 314 has asufficiently large capacitance in order to minimize pacing pulse droop.In one embodiment, the second coupling capacitor 314 has a capacitanceof greater than 10 microfarads. In an additional embodiment, the firstcoupling capacitor 312 has a capacitance that is less than the secondcoupling capacitor 314. In one embodiment, the first coupling capacitor312 has a capacitance of less than 5 microfarads. The first couplingcapacitor 312 is selectively employed, via switch 308 to selectivelyreduce the effective capacitance of the second coupling capacitor 314,thereby quickly attenuating the polarization voltage or “afterpotential”resulting from pacing delivered between electrodes 320 and 322.

In operation, the pacing output circuit 300 performs a charging cycle, apacing cycle and a recharge cycle. During the charging cycle, switch 302is closed and switches 304-308 are open to charge capacitor 310. Duringthe pacing cycle, energy for pacing is supplied from the capacitor 310by opening switches 302 and 306 and closing switches 304 and 308.Voltage is then discharged through the second coupling capacitor 314 tothe electrodes 320 and 322. By bypassing the first coupling capacitor312, the second coupling capacitor 96 is at its full capacitance level.This serves to effectively block DC signals from reaching the heart.During the recharging cycle, switches 302 and 304 are open and switch306 is closed. This allows the circuit 300 to passively recharge as thecharge within the heart flows back into the circuit 300 to balance out.During this passive recharge period, the charge on the second couplingcapacitor 314 may be such that the afterpotential signal exponentiallydecays over a relatively long period of time (e.g., lasting up to 100milliseconds). This large “afterpotential” signal masks any evokedresponse of the heart from the pacing pulse. This is because the evokedresponse from the heart typically occurs within 20 milliseconds fromdelivery of the stimulus pulse and are smaller in magnitude than thelarge “afterpotential” which would develop within the second couplingcapacitor 314 if it were not attenuated. Attenuation of theafterpotential is achieved by having the switch 308 in the open statesuch that the first coupling capacitor 312 and second coupling capacitor314 are connected in series. Series coupling of capacitors 312 and 314causes the overall capacitance to approximate the lower capacitance(i.e., the capacitance of the first capacitor 312). This lower effectivecapacitance quickly attenuates the polarization voltage or“afterpotentials” which results immediately following the application ofa stimulation pulse such that the evoked response of the heart will notbe buried or masked within the afterpotential. This in turn allows forthe identification of an evoked response (or capture) of the heart.

Referring again to FIG. 2, at 240, when the cardiac depolarizationdetected from the second cardiac region is identified as occurring indirect reaction to the electrical pulse delivered to the first cardiacregion in 220, the first value of the electrical pulses is modified. Inone embodiment, the first value of the electrical pulses is lowered by afirst amount when the cardiac depolarization in the second cardiacregion occurs in direct reaction to the electrical pulse delivered tothe first cardiac region. Alternatively, the first value of theelectrical pulses is lowed by a first percentage of the voltage value.In one embodiment, the value of the electrical pulses is lowered byapproximately two tenths (0.2) volts. Alternatively, the firstpercentage of the voltage value is in a range of approximately 5 to 20percent.

Referring now to FIG. 4, there is shown an additional embodiment of themethod for the present subject matter. For the embodiment of FIG. 4, thefirst cardiac region is a supraventricular location of the heart, fromwhich an atrial cardiac signal is sensed. By way of example, and not byway of limitation, the supraventricular location includes a locationwithin the coronary sinus vein, where the atrial cardiac signal containsindications of atrial contraction events. Additionally, the secondcardiac region is a ventricular region of the heart, where the one ormore electrodes located within the supraventricular location are used tosense cardiac activity from the second cardiac region (e.g., theventricular region of the heart). Alternatively, additional electrodesare implanted either in a right ventricle location or a locationadjacent the left ventricle of the heart, accessed through the coronarysinus/great cardiac vein, from which a ventricular cardiac signal issensed. The ventricular cardiac signal contains indications ofventricular contraction events which are then used in the presentsubject matter. In an alternative embodiment, the labels given to thecardiac signals sensed from the atrial and ventricular regions of theheart can be reversed for the present subject matter, such that thefirst cardiac region is the ventricular region of the heart asdescribed, while the second cardiac region is the atrial region of theheart, as described.

At 400, electrical pulses having a first value are delivered to thesupraventricular location. In one embodiment, the first value of theelectrical pulses is the first voltage value as previously described.Alternatively, the first value is the width of an electrical pulse, aspreviously described. At 420, a cardiac signal is sensed and analyzed todetect indications of cardiac depolarizations from the ventricularcardiac region that occur as a direct reaction to the electrical pulsedelivered to the supraventricular location. In one embodiment, thecardiac depolarization occurring in the ventricular region as a directreaction to a pulse delivered to the supraventricular region isidentified as previously described. At 440, when the cardiacdepolarization detected from the ventricular cardiac region isidentified as occurring in direct reaction to the electrical pulsedelivered to the supraventricular region, the first value of theelectrical pulses is modified. In one embodiment, the first value of theelectrical pulses is lowered by a first amount or percentage, aspreviously described, when the cardiac depolarization in the ventricularcardiac region occurs in direct reaction to the electrical pulsedelivered to the supraventricular cardiac region.

Referring now to FIG. 4, there is shown one embodiment for determiningthe first value of the electrical pulses delivered to the first cardiacregion. In one embodiment, the process tests the threshold voltagerequired to capture the atria and the threshold voltage required tocapture the ventricles. An average voltage of these two thresholdvoltages is then used as the first value of the electrical pulsesdelivered to the first cardiac region.

By way of example, and not by way of limitation, the process of testingthe threshold voltages, or pulse widths, required to capture the atriaand the ventricles can be accomplished with either a “step-up” or a“step-down” pacing protocol. The testing of the atria and ventricularthresholds is conducted at a first time interval. In one embodiment, thethreshold testing is programmed to occur at any time from an hourlybasis to a daily basis. Alternatively, other indicators/sensors from thecardiac rhythm management system can be used to trigger the thresholdtesting. For example, when beat-to-beat atrial autocapture is available.

FIG. 5 shows one example of a threshold test employing a step-upprocedure. At 500, the first time interval is tested to determine if ithas expired. When the first time interval has not expired, the systemreturns to 500 to make the next inquiry. When the first time intervalhas expired, however, the test moves to 510. At 510, a series of testpacing pulses are delivered to the first cardiac region, where eachpacing pulse in test pacing pulses are delivered at a first value whichvaries over a first value range. In one embodiment, the first valuerange is a programmable range, where one range which can be used is fromabout 1 volt to 10 volts.

Initially, one or more pacing pulses of the test pacing pulses aredelivered at an initial low-test pacing pulse, where the initiallow-test pacing pulse is the pacing pulse with the lowest value in thefirst value range (e.g., has the lowest voltage value of the pacingpulses in the first value range). As the pacing pulse is delivered, theone or more cardiac signals are analyzed to detect the occurrence ofcardiac depolarizations from the first cardiac region and/or the secondcardiac region as a result of the pacing pulse (e.g., the initiallow-test pacing pulse).

In one embodiment, the initial low-test pacing pulses will not causeeither the first or second cardiac region to depolarize. At 520, thefirst value of the test pacing pulses is then increased incrementallyover the first value range until the first cardiac region is depolarizedand the second cardiac region is not depolarized by the test pacingpulses. The first value of the pacing pulse which causes this to happenis referred to as a first cardiac region pacing threshold value. At 530,the values of the test pacing pulses are then incrementally increasedover the first value range until a second cardiac region pacingthreshold value is reached. At this point, both the first cardiac regionand the second cardiac region are depolarized by the test pacing pulses.In one embodiment, the incremental increase of the test pacing pulse isa programmable value in the range of 0.1 to 0.5 volts.

The first value of the electrical pulses to be delivered to the firstcardiac region are then set based on the threshold test at 540. In oneembodiment, the value of the electrical pulses to be delivered to thefirst cardiac region are set to a value that is based on the first andsecond cardiac region pacing threshold values. For example, the firstvalue of the electrical pulses is set to a value that is between thefirst cardiac region pacing threshold value and the second cardiacregion pacing threshold value. By way of further example, the firstvalue of the pulses could be set to a value that is midway (an averageor median value) between the first and second cardiac region pacingthreshold values.

In an additional embodiment, a safety margin value is added to the firstvalue calculated from the first and second cardiac region pacingthreshold values. The safety margin accommodates for variations orchanges in the pacing threshold of the first cardiac region. In oneembodiment, the safety margin value is an additional amount of, forexample, voltage or pulse width which is added to the first valuecalculated from the first and second cardiac region pacing thresholdvalues. For example, the safety margin is a programmable value in therange of 0.1 to 0.8 volts, where 0.5 volts is one value that can beused. In an alternative embodiment, the safety margin is a firstpercentage of the calculated first value, where the first percentage isset in a range from 8 to 20 percent (%), where 20 percent is one valuethat can be used.

As discussed above, once the first value for the electrical pulsedelivered to the first cardiac region is set, the at least one cardiacsignal is monitored to detect the occurrence of a cardiac depolarizationin the second cardiac region that is in direct reaction to theelectrical pulse delivered to the first cardiac region. When anelectrical pulse is determined to have caused a cardiac depolarizationin the second cardiac region, the first value (e.g., voltage, pulsewidth) of the electrical pulse is lowered, as previously described,until cardiac depolarizations in the second cardiac region occurring indirect reaction to the electrical pulse are no longer detected. Oncethis occurs, the system will proceed to use this value of the electricalpulse until the sensed cardiac signals indicate the value needs to bechanged. In an additional embodiment, if a situation develops where thefirst value of the electrical pulses drops to the point where the firstcardiac region is not being captured by the electrical pulses delivered,but the second cardiac region continues to be captured by the electricalpulses, the protocol of the present subject matter discontinuesdelivering the electrical pulses to the first cardiac region.

Referring now to FIG. 6, there is shown one example of the thresholdtest employing a step-down procedure. At 600, the first time interval istested to determine if it has expired. When the first time interval hasnot expired, the system returns to 600 to make the next inquiry. Whenthe first time interval has expired, however, the test moves to 610. At610, a series of test pacing pulses are delivered to the first cardiacregion, where each pacing pulse in test pacing pulses are delivered at afirst value which varies over a first value range. Initially, one ormore pacing pulses of the test pacing pulses are delivered at an initialhigh-test pacing pulse, where the initial high-test pacing pulse is thepacing pulse with the highest value in the first value range (e.g., hasthe highest voltage value of the pacing pulses in the first valuerange). As the pacing pulse is delivered, the one or more cardiacsignals are analyzed to detect the occurrence of cardiac depolarizationsfrom the first cardiac region and/or the second cardiac region as aresult of the pacing pulse (e.g., the initial high-test pacing pulse).

In one embodiment, the initial high-test pacing pulses causes both thefirst or second cardiac region to depolarize. At 620, the value of thetest pacing pulses is then reduced incrementally over the first valuerange until the first cardiac region is depolarized, but the secondcardiac region is no longer depolarized by the test pacing pulses. Thevalue of the pacing pulse which causes this to happen is referred to asa second cardiac region pacing threshold value. At 630, the values ofthe test pacing pulses are then incrementally reduced over the firstvalue range until a first cardiac region pacing threshold value isreached where both the first cardiac region and the second cardiacregion are no longer depolarized by the test pacing pulses. The firstvalue of the electrical pulses to be delivered to the first cardiacregion are then set based on the threshold test at 640, as previouslydiscussed for the threshold test employing a step-up procedure.

The present subject matter is useful for cardiac rhythm managementsystems having electrodes located in or around the atria, includingelectrodes located in the coronary sinus vein and/or the great coronaryvein for the purpose of pacing the atrium. The present subject mattercan also be used with system which also have electrodes located in theventricles and systems which use autocapture algorithms to detect andidentify cardiac depolarizations in the atrium and the ventricles.

Referring now to FIG. 7, there is shown a schematic of a cardiac rhythmmanagement system 700 according to the present subject matter. In thepresent embodiment, the cardiac rhythm management system 700 includes anelectrode system which includes a first cardiac lead 702 having at leastone electrode 704. In one embodiment, the electrode 704 is a pace/senseelectrode located at or near a distal end 706 of the first cardiac lead,where the electrode 704 is used to sense either unipolar cardiac signals(electrode and housing 708 of the system 700) or bipolar cardiac signals(when an additional electrode is in proximity to electrode 704). In oneembodiment, the cardiac rhythm management system 700 includes controlcircuitry coupled to the at least one electrode 704 from which a firstcardiac signal is sensed and from which the present subject matter isperformed.

In the embodiment of FIG. 7, the first cardiac region is an atrialregion 710 and the second cardiac region is a ventricular region 712.The first cardiac lead 702 is shown implanted in the supraventricularregion of the heart, where the distal tip of the lead 702 is positionedin the coronary sinus vein 714. In one embodiment, the electrode 704 atthe distal tip of lead 706 is positioned adjacent the left atrium 716 ofthe heart 718. From this location, the unipolar signal sensed betweenthe electrode 704 and the housing 708 will contain indications ofcardiac depolarizations (e.g., P-waves) from the atrium and cardiacdepolarizations that occur in the ventricles (e.g., R-waves orQRS-complexes). In one embodiment, the electrode 704 is implanted in thecoronary sinus 714 to provide for sensing and pacing to the atria andsensing from the ventricle. In this embodiment, the first cardiac regionis the atria of the heart, while the second cardiac region is theventricles of the heart. In an alternative embodiment, the electrode 704is implanted in the coronary sinus 714 to provide for sensing and pacingto the ventricles (e.g., from a position adjacent the left ventricle)and sensing from the atrium. In this embodiment, the first cardiacregion is the ventricles of the heart, while the second cardiac regionis the atria of the heart.

In addition to providing electrode 704, additional electrodes can bepositioned on the first cardiac lead 702. For example, one or moreadditional pacing/sensing electrodes and/or defibrillation coilelectrodes can be located on the first cardiac lead to allow for anycombination of unipolar and/or bipolar sensing between the electrode 704and the additional electrode(s). Use of these additional electrodes thenprovides for a variety of possible sensing and shocking (e.g., pacingpulses) vectors between the electrodes themselves and/or the housing 708of the cardiac rhythm management system 700. In an additionalembodiment, the electrode system further includes a second cardiac lead,where the second cardiac lead includes one or more electrodes(pace/sense electrodes and/or defibrillation electrodes) and isimplanted with one or more of the electrodes located in the rightventricular chamber to allow for cardiac depolarizations from theventricles to be detected. Additionally, the first cardiac lead 702 canbe of a length to allow the distal end 706 of the lead to be positionedadjacent the left ventricle (e.g., via the great cardiac vein) with theelectrode 704 positioned on the lead body to allow the electrode 704 tobe positioned between the left atrium 716 and the left ventricle (samerelative position as shown in FIG. 7) and one or more additionalelectrodes positioned at or near the distal end 706 so as to place theadditional electrodes adjacent the left ventricle.

FIG. 7 also shows a medical device programmer 734. The medical deviceprogrammer 734 and the cardiac rhythm management system 700 includecommunication circuitry which allows for cardiac data to be to and fromthe cardiac rhythm management system 700. In addition, command signalsfor controlling the operation of the cardiac rhythm management system700 can also be sent between the medical device programmer 734 and thecardiac rhythm management system 700. In one embodiment, communicationbetween the medical device programmer 734 and the cardiac rhythmmanagement system 700 is established over a radio frequency telemetrychannel, as is known in the art.

Referring now to FIG. 8, there is shown one embodiment of a cardiacrhythm management system according to the present subject matter. Thesystem includes an implantable cardiac rhythm management device 800, afirst cardiac lead 802 and a second cardiac lead 804. In one embodiment,both the first cardiac lead 802 and the second cardiac lead 804 includeat least one electrode each. In the embodiment shown in FIG. 8, thefirst cardiac lead 802 includes a first ventricular electrode 806, afirst atrial electrode 808 and a second atrial electrode 810. The secondcardiac lead 804 is shown including a first ventricular electrode 812and a second ventricular electrode 814.

FIG. 8 shows an embodiment in which the first ventricular electrode 806,the first atrial electrode 808 and the second atrial electrode 810 ofthe first cardiac lead 802 are ring electrodes (either partially orcompletely encircling the peripheral surface of the cardiac lead). FIG.8 also shows the first ventricular electrode 812 being located at thedistal end/tip of the second cardiac lead 804 and the second ventricularelectrode 814 being a ring electrode (either partially or completelyencircling the peripheral surface of the cardiac lead). However,additional electrode structures could be used, and are considered withinthe scope of the present invention.

In one embodiment, the first cardiac lead 802 is implanted within theheart, where the distal end of the lead 802 is implanted through thecoronary sinus vein and the great cardiac vein to allow the firstventricular electrode 806 to be positioned adjacent the left ventricularchamber of the heart. In one embodiment, the first ventricular electrode806 is used in conjunction with the housing 820 and/or an indifferentelectrode 822 mounted on the implantable cardiac rhythm managementdevice 800 to sensed, or detect, a cardiac signal (near field signal)from the heart. In addition, when implanted the first atrial electrode808 and the second atrial electrode 810 are positioned insupraventricular region within the coronary sinus. In one embodiment,the first and second atrial electrodes, 808 and 810, are used to sense,or detect, a cardiac rate signal (near field signal) from the heart.Additionally, the second cardiac lead 804 is implanted within the heart,where the distal end of the lead 804 is implanted at the apex of theright ventricle to allow the first ventricular electrode 812 and thesecond ventricular electrode 814 to be implanted within the rightventricular chamber of the heart. In one embodiment, the first andsecond ventricular electrodes, 812 and 814, are used to sensed, ordetect, a cardiac rate signal (near field signal) from the heart.

The electrodes are connected to electronic circuitry within theimplantable cardiac rhythm management device 800 through lead conductorshoused and electrically insulated within the body of the first andsecond cardiac leads 802 and 804. The lead conductors are coupled tolead connectors on the cardiac leads, which allow for the electrodespositioned on the leads to be coupled to the electronic circuitrythrough input terminals 824, 826, 828, 830 and 832. In one embodiment,the first and second cardiac leads 802 and 804 have elongated bodiesmade of one or more materials suitable for implantation in a human body,where such materials are known in the art. Additionally, the electrodesare constructed of electrically conductive materials, such as platinum,platinum-iridium alloys, or other alloys as are known. The leadconductors are also constructed of electrically conductive materialssuch as MP35N, an alloy of nickel, chromium, cobalt, and molybdenum.

The implantable cardiac rhythm management device 800 includes controlcircuitry 840, where the control circuitry 840 is coupled to theelectrodes 806, 808, 810, 812 and 814, from which at least a firstcardiac signal is sensed, generates electrical energy pulses underpredetermined conditions, and delivers electrical energy to electrodespositioned on the leads under the predetermined conditions.

In one embodiment, the control circuitry 840 is a programmablemicroprocessor-based system, with a microprocessor 842 and a memorycircuit 844, which contains parameters for various pacing and sensingmodes and stores data indicative of cardiac signals received by thecontrol circuitry 840. The control circuitry 840 further includes apulse circuit 846, a depolarization circuit 848 and a pulse adjustmentcircuit 850 which are coupled to each other and the microprocessor 842and memory circuit 844 through bus 852. In one embodiment, the pulsecircuit 846 is the pacing output circuit as previously described.

The implantable cardiac rhythm management device 800 further includes anevoked response sensing amplifier 860, where the amplifier 860 includesa first switch 854 and a second switch 856, under the control ofmicroprocessor 842, to allow the amplifier 860 to be switched betweenvarious sensing configurations. In one embodiment, the amplifier 860 isused in conjunction with the pacing output circuit and autocaptureprotocols which are executed by the control circuitry 840 of theimplantable cardiac rhythm management device 800. In one embodiment, theuse of the evoked response sensing amplifier 860 allows for (1) sensingbetween either the first or second atrial electrode, 808 or 810, and thehousing 820 or the indifferent electrode 822; (2) sensing between thefirst ventricular electrode 806 and the housing 820 or the indifferentelectrode 822; (3) the first ventricular electrode 812 and the housing820 or the indifferent electrode 822; and (4) for sensing between thefirst and second ventricular electrodes, 812 and 814.

In addition to the evoked response sensing amplifier 860, theimplantable cardiac rhythm management device 800 further includesamplifier 862 and 864. In one embodiment, first and second ventricularelectrodes, 812 and 814, are coupled to amplifier 862 to allow for abipolar signal to be sensed between the electrodes. In addition, firstand second atrial electrodes, 808 and 810, are coupled to amplifier 864to allow for a bipolar signal to be sensed between the electrodes.

Generally, the pulse circuit 846 is coupled to at least one electrodeand produces electrical pulses at the first value to be delivered to theat least one electrode in the first cardiac region, as previouslydescribed. In the embodiment shown in FIG. 8, the pulse circuit 846 isshown coupled to the electrodes 806, 808, 810, 812 and 814, where thepulse circuit 846 can generate electrical pulses at the first value tobe delivered to any combination of the electrodes 806, 808, 810, 812 and814 under the control of the control circuitry 840. Power to theimplantable cardiac rhythm management device 800 is supplied by anelectrochemical battery 870 that is housed within the device 800.

The output of each of the amplifiers 860, 862 and 864 is coupled to thedepolarization circuit 848. As previously discussed, a first cardiacsignal is sensed from which the occurrence of cardiac depolarizations isdetected. In the present embodiment, the first cardiac signal is sensedfrom any combination of the first atrial electrode 808, the secondatrial electrode 810 and the housing 820, such that the first cardiacregion is an atrial region of the heart. In addition to detectingcardiac depolarizations which occur in the atrial region, the firstcardiac signal will also contain indications of cardiac depolarizationswhich occur in the ventricles. From this, the depolarization circuit 848can detect in the first cardiac signal any occurrence of cardiacdepolarizations in the second cardiac region that occur in directreaction to electrical pulses generated by the pulse circuit 846. Aspreviously discussed, autocapture protocols are executed in the controlcircuitry 840 to monitor the capture of both atrium and ventriclechambers in response to electrical energy supplied to the one or moreelectrodes positioned in or around the coronary sinus vein.

As previously discussed, when a second cardiac region depolarizes as adirect reaction to electrical pulses delivered to a first cardiac region(e.g., pulses delivered to the stimulate the atrial region whichinstead, or additionally, stimulate the ventricular region) the presentsubject matter changes the first value of the electrical pulses. Theembodiment shown in FIG. 8, the pulse adjustment circuit 850 modifies,or adjusts, the values of the electrical pulses when the depolarizationcircuit 848 detects the occurrence of a cardiac depolarization in thesecond cardiac region that occurs in direct reaction to an electricalpulse delivered in the first cardiac region. In one embodiment, thedepolarization circuit 848 utilizes the autocapture protocols previouslydiscussed to detect and identify the occurrence of cardiacdepolarizations in the second cardiac region that occurs in directreaction to electrical pulses delivered in the first cardiac region.

In one embodiment, when the depolarization circuit 848 detects theoccurrence of the cardiac depolarization in the second cardiac regionthat occurs in direct reaction to the electrical pulse delivered to theat least one electrode in the first cardiac region, the pulse adjustmentcircuit 850 lowers the first value (e.g., voltage or pulse width) of theelectrical pulses by the first amount, as previously discussed. Inaddition, the pulse adjustment circuit 850 sets the first value of theelectrical pulses based on the previously discussed threshold test.

In one embodiment, the threshold test is conducted by the controlcircuitry 840, where the pulse circuit 846 delivers test pacing pulsesat values over a first value range to at least one electrode. In oneembodiment, the at least one electrode is either the first atrialelectrode 808 or the second atrial electrode 810. As previouslydiscussed, the first value range includes an initial step-down pacingpulse for which the depolarization circuit 848 detects a depolarizationin the first cardiac region and the second cardiac region. During thestep-down pacing pulse, the values of the test pacing pulses are reducedover the first value range at first intervals until the second cardiacregion is no longer depolarized by the test pacing pulses. As previouslydiscussed, this pacing pulse value is referred to as the second cardiacregion pacing threshold value. The test pacing pulses are continued tobe reduced by the control circuitry 740 until the first cardiac regionis no longer depolarized by the test pacing pulses. As previouslydiscussed, this pacing pulse value is referred to as the first cardiacregion pacing threshold value. The pulse adjustment circuit 750 thensets the first value based on the first cardiac region pacing thresholdvalue and the second cardiac region pacing threshold value in a manneras previously discussed. In a similar fashion, the control circuitry 840controls the delivery of the step-up pacing pulses in the thresholdtest, as previously discussed, so as to set the first value based on thefirst cardiac region pacing threshold value and the second cardiacregion pacing threshold value.

Electronic communication circuitry 874 is additionally coupled to thecontrol circuitry 840 to allow communication with an external controller866. In one embodiment, the electronic communication circuitry 874includes a data receiver and a data transmitter to send and receive andtransmit signals and cardiac data to and from an external programmer866. In one embodiment, the data receiver and the data transmitterinclude a wire loop antenna to establish a radio frequency telemetriclink, as is known in the art, to receive and transmit signals and datato and from the programmer unit 866.

This application is intended to cover any adaptations or variations ofthe present invention. It is manifestly intended that this invention belimited only by the claims and equivalents thereof.

1. A system configured to be coupled to a heart, the system comprising:an implantable cardiac rhythm management device including: a pacingoutput circuit configured to generate first electrical pulses at a firstvalue for delivery to the heart; an evoked response sensing amplifierconfigured to sense a first evoked response and a second evokedresponse, the first and second evoked responses each evoked by one ofthe first electrical pulses at the first value; a depolarization circuitconfigured to receive from the evoked response sensing amplifier anamplified signal indicative of the sensed first and second evokedresponses and detect a first cardiac depolarization and a second cardiacdepolarization using the amplifier signal, the first and second cardiacdepolarizations each occurring in direct reaction to the one of thefirst electrical pulses at the first value; and a pulse adjustmentcircuit coupled to the depolarization circuit and the pacing outputcircuit, the pulse adjustment circuit configured to adjust the firstvalue depending on whether the first cardiac depolarization is detectedand whether the second cardiac depolarization is detected.
 2. The systemof claim 1, wherein the implantable cardiac rhythm management devicecomprises switches coupled to the evoked response sensing amplifier, theswitches configured to allow the evoked response sensing amplifier toreceive a first signal from which the first evoked response is sensedand a second signal from which the second evoked response is sensed. 3.The system of claim 1, further comprising an electrode system, whereinthe implantable cardiac rhythm management device comprises switchescoupled between the electrode system and the evoked response sensingamplifier, the switches configured to allow the evoked response sensingamplifier to be switched between various sensing configurations eachusing electrodes selected from the electrode system.
 4. The system ofclaim 3, wherein the electrode system comprises a housing of theimplantable cardiac rhythm management device, the housing connected toone of the switches to be used for the sensing of at least one of thefirst and second evoked responses.
 5. The system of claim 3, wherein theelectrode system comprises an indifferent electrode mounted on theimplantable cardiac rhythm management device, the indifferent electrodeconnected to one of the switches to be used for the sensing of at leastone of the first and second evoked responses.
 6. The system of claim 3,wherein the electrode system comprises intracardiac electrodes eachconnected to one of the switches to be used for the sensing of at leastone of the first and second evoked responses.
 7. The system of claim 1,wherein the pacing output circuit comprises: a first coupling capacitorto block DC signals from reaching the heart; a second coupling capacitorconnected in series to the first coupling capacitor; and a switchconnected in parallel to the second coupling capacitor to allow aselective employment of the second coupling capacitor.
 8. The system ofclaim 7, wherein the first coupling capacitor has a capacitance greaterthan ten microfarads, and the second coupling capacitor has acapacitance less than five microfarads.
 9. A method for pacing a heart,the method comprising: delivering first electrical pulses at a firstvalue to the heart; receiving a first signal and a different secondsignal; detecting a first evoked response from the first signal and asecond evoked response from a second signal, the first and second evokedresponses each evoked by one of the first electrical pulses at the firstvalue; and adjusting the first value depending on whether the firstevoked response is detected and whether the second evoked response isdetected.
 10. The method of claim 9, wherein detecting the first andsecond evoked responses comprises using a single evoked response sensingamplifier coupled to switches allowing the evoked response sensingamplifier to receive the first signal from and the second signal. 11.The method of claim 10, wherein delivering the first electrical pulsecomprises delivering the first electrical pulse to a first cardiaclocation, and detecting the first and second evoked responses comprisesdetecting the first evoked response from the first cardiac location anddetecting the second evoked response from a second cardiac location. 12.The method of claim 11, wherein delivering the first electrical pulsecomprises delivering the first electrical pulse to a supraventricularlocation, and detecting the first and second evoked responses comprisesdetecting the first evoked response from the supraventricular locationand detecting the second evoked response from a ventricular location.13. The method of claim 9, wherein detecting the first and second evokedresponses comprises reducing a coupling capacitance during the deliveryof the first electrical pulse to the heart, the coupling capacitanceused to block DC signals from reaching the heart.
 14. The method ofclaim 13, wherein the coupled capacitance is provided by a firstcoupling capacitor connected in series with a second coupling capacitor,and reducing the coupling capacitance comprises opening a switchconnected in parallel to the second coupling capacitor.
 15. A method forpacing a heart, the method comprising: delivering first electricalpulses at a first value to the heart; determining a first pacingthreshold by adjusting the first value and detecting first evokedresponses each evoked by one of the first electrical pulses; determininga second pacing threshold by adjusting the first value and detectingsecond evoked responses each evoked by one of the first electricalpulses; and setting the first value using the first pacing threshold andthe second pacing threshold.
 16. The method of claim 15, whereindetermining the first pacing threshold comprises increasing the firstvalue until the first evoked responses are detected, and determining thesecond pacing threshold comprises increasing the first value until thesecond evoked responses are detected.
 17. The method of claim 15,wherein determining the second pacing threshold comprises decreasing thefirst value until the second evoked responses are detected, anddetermining the first pacing threshold comprises decreasing the firstvalue until the first evoked responses are detected.
 18. The method ofclaim 15, wherein detecting the first evoked responses comprises usingan evoked response sensing amplifier coupled to a first cardiac locationthrough a switch, and detecting the second evoked responses comprisesusing the evoked response sensing amplifier coupled to a second cardiaclocation through another switch
 19. The method of claim 18, whereinadjusting the first value comprises adjusting a pacing voltage.
 20. Themethod of claim 18, wherein adjusting the first value comprisesadjusting a pacing pulse width.
 21. The method of claim 18, whereinsetting the first value comprises setting the first value to an averageof the first pacing threshold and the second pacing threshold.